This invention relates to stereoscopic (stereo) hardcopy image generation and viewing methods, and mainly to methods for producing said hardcopy from a computer controlled printer. This application is related to Disclosure Document 260862 filed in the Patent and Trademark Office on Aug. 16, 1990. The contents of Disclosure Document 260862 are hereby incorporated by reference herein.
Computer-based workstations that are currenfiy available provide a display to the user on a display monitor. Some workstations that are currently available display a full color, high quality, stereoscopic image to a user who is equipped with appropriate glasses for discriminating two stereo perspective views (SPVs) generated by the display monitor. Typically, the display monitor operates so that the left eye SPV is displayed with left-handed circularly polarized light (CPL) and the right eye SPV is displayed with right-handed CPL, and the left lens of the user's glasses transmit only left-handed CPL and the right lens transmits only right-handed CPL.
The image that is displayed on the monitor of a workstation is ephemeral. If a particular image is to be preserved, it is necessary to make a hardcopy of the image. Such a hardcopy is generated by use of a printer that is connected to the workstation. Printing technologies that are in common usage for graphics and imaging do not generate stereoscopic images, and accordingly the hardcopy generated by a workstation printer is monoscopic in nature. There are six printer technologies in common usage for graphics and imaging: The impact printers (Dot Matrix, Daisy Wheel, etc.), the ink jet printers, the phase change printers, the laser printers, the thermal wax printers and the dye sublimation printers.
The impact printers use hammers to transfer ink from a ribbon to the print medium. The Dot Matrix printers use, as the name implies, a matrix of dots to form print characters and other print detail whereas the Daisy Wheel and related printers, transfer entire characters from the ribbon to the media. It is usual for these printers to print only in black or a single color and the writing speed is slow.
The ink jet printer has become very popular because of its high quality prints and modest costs, particularly regarding color. These printers squirt a droplet of ink through an orifice onto the print medium to form a written dot and through a process of connecting the dots, write characters and other print detail. There are two basic methods of squirting the ink in these machines. The first is the piezoelectric driver, where a piezoelectric material produces a mechanical motion or displacement in the ink jet cavity when driven by an electrical pulse. This displacement pressurizes the cavity and thus pushes an ink droplet through the cavity orifice and onto the print medium. The second method uses a minute heating element to vaporize a small amount of the ink in the ink jet cavity, thus pressurizing the cavity and squirting ink through the ink jet orifice onto the medium. Depending upon the degree of ink jet multiplexing used, these printers vary from having slow to moderate writing speeds.
The third printer technology is Phase Change Printing (PCP), where a solid (colored wax) is heated until it melts and then this ink is deposited by basic ink jet methods (piezoelectric divers). The warm wax is then pressed into the print medium with a roller. The print quality of these printers is excellent and because of a high degree of printhead multiplexing, the writing speed is also very good.
The technology of the laser printer is well documented. In general the process consists of negatively charging a photosensitive drum and then, when one or more light beams (laser or LED) strikes (writes) the drum, the written areas become positively charged and when exposed to a negatively charged plastic toner powder, the toner is transferred to the positively charged areas on the drum, then, positively charged paper is passed by the drum, attracting the toner powder to the paper which is then passed through heated rollers to fuse the toner onto the paper. Color laser printers use essentially the same process, which is repeated four times for the colors of cyan, magenta, yellow and black, and the toners are not fused until after all the toners are deposited. Laser printers offer excellent print quality and writing speed.
The thermal wax printer uses a ribbon with page size areas of cyan, magenta and yellow wax layers upon it. Black wax areas are sometimes also used. The colored areas of the ribbon sequentially overlay the print medium, whereupon wax from the ribbon is transferred to the medium by heating the wax in the areas where the transfer is to be performed. This process is very wasteful of printing consumables. The print quality is excellent, while the printing speed is slow.
The dye sublimation print process is essentially the same as the thermal wax process, other than the fact that a dye, rather than a wax, is transferred from the ribbon to the medium by vaporization rather than melting.
None of the computer printing systems thus far discussed have the ability to rapidly create a high quality color hardcopy of the stereoscopic display from a computer terminal or workstation.
However stereo hardcopy is possible by the archaic methods of the anaglyph, Vectograph.RTM. and prismatic technologies, including the parallax barrier.
The anaglyph is the familiar two color (commonly cyan & red) stereo method of the movies and print media. These can be easily generated on the existing computer printers, but the anaglyphs lack color integrity and the glasses which must be worn, are not compatible with the glasses worn for the computer's stereo display, nor are they cosmetically appealing.
Vectograph.RTM. is a product of Polaroid Corporation and consists of stretched PVA layers, oriented orthogonally on each side of a transparent supporting medium. The stretched PVA layers will form orthogonal linear polarizers when treated with certain iodine salts. An ink is made of potassium iodine (KI) desolved in water and a Stereo Perspective View (SPV) is printed on each side of the Vectograph with this ink. This printing is usually done using photolithographic type film (Kodak Matrix Film Type 4150 or Polaroid Vectograph Film R-1), which is soaked in the ink, drained and then impressed upon the Vectograph with rollers. Steps are then taken to fix and preserve the images. The result of this process is black & white stereo hardcopy when viewed through linearly polarizing glasses, having orthogonally oriented polarizing lenses. If a quarter wave plate with its optical axis at 45 deg. to the polarization axes, is placed over the Vectograph, circular polarizing glasses of the type worn to view the stereo display of a workstation can be used. Color Vectographs can also be made by repeating this process three times with filters used in exposing the photolithographic film and using polarizing color dyes to treat the Vectograph layers. And while the results of all this processing can be impressive, it does not lend itself to the timely generation of hardcopy from a computer terminal or workstation.
Prismatic techniques have been greatly refined over a period of forty or more years. This technique consists of covering the hardcopy medium with a linear array of lenticular lenslets or minute refracting prisms, such that when a given lenslet is viewed with left and rignt eyes a viewer sees information coming from differing areas of the hardcopy, due to the lens action and the lateral separation of the eyes. In this way, when the individual eyes are properly located relative to the hardcopy and the individual lenslets, a stereoscopic view can be presented to the viewer and if there is sufficient resolution in the hardcopy many SPVs can be presented as the viewer moves his head or rotates the hardcopy, thus allowing the impression of a true three dimensional display where the viewer can "look behind" objects in the foreground. Another advantage of the prismatic hardcopy is that it is autostereoscopic (requiring no glasses).
The parallax barrier is very similar to the prismatic hardcopy with the exception that rather than lenslets the barrier technique sets opaque stripes some small distance away from the printed surface, so that when the gaps between the stripes are viewed, each eye perceives a different portion of the printed surface and if this surface is printed such that each eye sees one of a stereo pair of images, the viewer will sometimes be able to fuse these images and perceive a stereoscopic display. The poor resolution and exacting registration requirements render the prismatic and the parallax barrier techniques unsuitable for computer generated hardcopy.
Thus, none of these hardcopy technologies will yield a high quality, color hardcopy from a standard or slightly modified computer printer.